The present invention relates to bead rings of package type reinforcing the beads of tires and produced by winding wires, preferably metallic wires of rectangular cross-section, over a body of revolution.
The present invention applies in particular to bead rings of the type mentioned above whose radially inner face is frustoconical and smooth, and which are manufactured by the process described in French Patent No. 2,456,610 (which corresponds to U.S. Pat. No. 4,305,769). This process consists essentially in imparting a permanent deformation to the steel wire by means of a suitable deviated flexion before it is wound on the manufacturing form. Thus, the wires which are juxtaposed in the same layer and superposed from one layer to the next are duly aligned with each other. As a result, therefore, the wires which have been treated in this way are free of residual elastic stresses and no longer have a tendency to unwind by themselves.
However, it is still necessary to assure the coherence of such a bead ring during the course of the handling of it, from the time when it is removed from the manufacturing form until the time that it is incorporated in the bead of the tire by the manufacturer of the latter, without loss of its flexibility or its resistance to rupture.
For this reason, in accordance with the present invention, in order to produce a package bead ring for tires having a rectangular radial cross-section and therefore a rectilinear radially inner face and formed of at least two layers of at least two adjacent wires, preferably metallic wires, of rectangular cross-section wound alongside each other from layer to layer and from wire to wire on a manufacturing form after permanent bending of the wires, there is used a process which is characterized by the fact that during the winding of the layers of wires a piece of ribbon, which is formed of a thin flexible support resistant to shear in the radial direction between two adjacent wires and which is of a thickness at most equal to 0.5 mm and preferably less than 0.3 mm, is interposed at irregular or regular intervals at least twice per revolution between two consecutive layers of wires, the support bearing on each of its faces a layer of a material which is adherent both to the support and to the wires.
Within the scope of the present invention, the support is formed of a film of paper or of either synthetic or metallic material, of a fabric (weft and warp) or of fibers or filaments oriented perpendicular to the direction of winding of the layers of wires on the manufacturing form for the bead ring, provided that the thickness of this support is at most equal to 0.5 mm and preferably less than 0.3 mm.
It is known to interpose a continuous layer of rubber solution between the turns of a bead ring formed by winding a wide steel ribbon (French Patent No. 1,281,439). The purpose of such a gluing is to avoid the sliding of the turns on each other, in particular upon the shaping of the tire into toroidal shape. However, the continuity of the layer of glue weakens the rupture load of such a bead ring, as has been shown by the research work of the applicant.
The present invention, by contrast, preserves not only the flexibility of the bead ring, as opposed to continuous gluing, but also the rupture load of the bead ring, which is the object of the improvement claimed, due to the slight thickness of the ribbons and their ratio to the surface of a layer of wires. Within the scope of the present invention, the total active surface of the pieces of ribbons interposed between two consecutive layers of wires is between 0.5% and less than 20% of the surface of one layer of wires counted over one revolution (length of one turn times width of one layer). Upon the winding of the layers of wires on the manufacturing form and the emplacing of the pieces of ribbon, it is preferable to provide for a staggering of the pieces of ribbon in the direction of the winding from one layer of wires to the next. In this way one avoids local excess thicknesses which are prejudicial to the rupture load of the bead ring and to the geometrical uniformity of its cross-section.
The thinness of the support of the pieces of ribbon in accordance with the invention, on the one hand, avoids the infiltration of the rubber between the wires and the layers of wires of the bead ring upon the vulcanizing of the tire and, on the other hand, assures that there is intimate contact between consecutive layers of wires over practically the entire surface of the wires. One thus assures the geometry of the bead ring without detriment to its rupture load.